Flat emitter

Abstract

A flat emitter comprises four current-supply heating legs. Half lighting for a small focus in which a current is supplied to heat only a region narrower and full lighting for a large focus in which a current is supplied to heat the entire region are selectable according to the combination of the legs. Either one of a set of the two full-lighting current-supply heating legs for the full lighting and a set of the two half-lighting current-supply heating legs for the half lighting is linearly formed, and the other is formed to be bent plural times in zigzag to set the space between the full-lighting current-supply heating leg and the half-lighting current-supply heating leg, which are adjacent to each other, at their terminals to be larger than the space at their base parts.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a flat emitter used for an electron source for an X-ray tube or for an electron source for another use, and more particularly to a technique of controlling lighting with four current-supply heating legs.[0003]2. Description of the Related Art[0004]An X-ray apparatus using an X-ray tube reduces a focal size of electrons upon X-raying or photographing a microscopic area, and enlarges a focal size upon X-raying or photographing a subject having a large body thickness in order to reduce a load to an anode. A structure is considered in which a plurality of emitters (also referred to as “filaments”) is prepared and each emitter is switched according to a purpose. However, preparing a plurality of emitters according to a purpose makes the structure complicated, and also increases the structure of the X-ray tube.[0005]In view of this, a single flat emitter that can form a plurality of focal spot...

AI Technical Summary

Benefits of technology

The present invention relates to a flat emitter for an electron source, which can be easily assembled to an X-ray tube or other electron source with high precision. The flat emitter has two full-lighting current-supply heating legs and two half-lighting current-suppply heating legs that are adjacent to each other. The space between the terminals of the adjacent legs can be made larger, increasing the distance between electrode bars for fixing the legs and improving electrical insulation. The flat emitter is designed to keep a balance and prevent deformation of the electron emission surface, ensuring high precision assembly and performance. The structure of the flat emitter is simplified, with linear formation of the legs, and a balance can be easily achieved.

Problems solved by technology

However, preparing a plurality of emitters according to a purpose makes the structure complicated, and also increases the structure of the X-ray tube.

If the flat emitter including the legs for the current supply and heating has a plate-like shape as illustrated in FIG. 7 or 8, there arise problems such that (1) a complicated mechanism is required to dispose the emitter relative to the electrode, and further, the work for disposing the emitter becomes complicated, and (2) the electron emission region (see the thermoelectrons B in FIG. 9) spreads to the legs upon an irradiation of high current, which fails to form a desired focal spot shape.

However, the structure of the double emitter type 1 has a problem of very small space between the electrode bars ER of the base as apparent from FIG. 13.

Therefore, it is extremely difficult to fix the electrode bars ER to the insulating member such as a ceramic while providing electrical insulation between the electrode bars ER.

However, this is not preferable from the viewpoint of strength.

Therefore, keeping balance is difficult, and the legs are difficult to be fixed to the base with high precision.

(1) The electron emission surface is deformed due to unnatural stress caused by the fixation, which fails to form a desired focal spot shape.

If the double emitter type 2 cannot be disposed with high precision, the focal spot might be enlarged or asymmetry might occur, entailing a problem in which a desired focal spot shape cannot be obtained.

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